Various structural possibilities are known from the prior art, in particular for use in the field of motor vehicle technology, to configure a motor housing, for an electric motor, in a multi-part manner. It is generally known, from the prior art, that a housing shell, which is cylindrical along at least part of its length, and adapted for receiving functional components of such an electric motor, can be so closed, with a housing cover assembly, that a motor shaft, of the electric motor accommodated in the housing, can be guided at one end through a bottom portion of the housing shell, a suitable first bearing being provided there for the shaft, while, axially opposite, the housing cover assembly can then either serve as, or receive, a second bearing for the shaft.
A preferred, but not exhaustive, use of such a category of technology, in the field of motor vehicle technology, relates to an electric motor which is used for implementing a so-called “active” or “power” steering and which is configured, in a manner otherwise known, for changing a transmission ratio of a motor vehicle and has, at a shaft end extending from the housing, a coupling to a worm drive or similar mechanical means.
The context of the automobile and/or motor vehicle technology, to be regarded as the preferred application area for the present invention, poses challenges with respect to mechanical construction, to mass production, and to reliable operation in everyday situations. For this reason, the initial requirement is that the respective structures, located on the housing shell end and on the housing cover assembly, for bearing support of the motor shaft, be so aligned with each other, as to achieve a best possible coaxiality. A deviation or tipping of these housing portions, away from the longitudinal axis of the motor shaft, would lead to negative consequences, such as excessive bearing friction, rough running of the motor, or the like.
It is also necessary to reduce the “play” of the motor shaft as much as possible, particularly in an environment which is frequently characterized by temperature fluctuations, different moisture conditions and potential contamination. Likewise, the motor housing, produced by connecting the housing shell to the housing cover assembly, is to be designed to be as mechanically stable as possible (with corresponding requirements for the stability of the connection between these components). The danger to be avoided is vibration, which leads to excessive noise and to potential failure modes. In addition, since the motor housing is potentially subjected, in a built-in and operating state, to forces both on the housing shell and on the housing cover assembly, the motor housing, once it is assembled and connected, must be able to transmit predetermined forces and torques.
For example, typical drive-side couplings of the electric motor, implemented in the motor housing, provide for a worm shaft, which is seated on the motor shaft, to be combined in a play-free manner and under pre-tensioning with a worm wheel of the further active steering assemblies, which places high demands on the coaxiality of the housing assemblies, in particular on that of the motor shaft bearings aligned by them.
It is known from the prior art, for example, to connect a housing shell to an associated housing cover assembly, by means of screwed or riveted connections. However, the frequently used screws have the disadvantage that they are driven, frictionally and usually with a certain (and unavoidable) play into one of the connecting partners, so that the above-described influences on the housing can, for example, cause a displacement of the connecting partners with respect to one another. The actual assembly process can itself bring about these disadvantages (even outside the context of motor operation in a motor vehicle).
On the other hand, the connecting technologies such as gluing, soldering or welding between the connecting partners, which are to be presumed to be equally common or known from the prior art, are disadvantageous for other reasons, for example: adhesive technology which is not unproblematic for long-term operation in a loaded motor vehicle environment, problems of achieving precision in a soldering or welding process, as well as high equipment investment needed to implement these technologies in a mass-production context.
This disadvantage is to be considered against the background, that the motor housing according to the invention, as a typical mass production product, should be adapted for automated production with a reproducible high quality of connection.